C.E.A. Grigorescu, H.J. Trodhal, N.M. Strickland, A.Bittar, S.A. Manea, J. Giapintzakis, O. Monnereau, R. Notonier, V.J. Kennedy, Minority-spin band parameters in a NiMnSb thin film determined by spectral conductivity, Journal of Applied Physics, 96/1 (2004) 6421-6424.

Abstract: NiMnSb is expected to be a ferromagnetic half metal, an expectation that is based in part on band structure calculations. Here we report optical conductivity studies of the band structure for a film prepared by pulsed laser deposition onto a Si substrate held at a relatively low temperature as is required for some device applications—films which are susceptible to site disorder associated with the vacant site in this half-Heusler compound. We demonstrate that the direct interband transitions are essentially unshifted in comparison with bulk material, though they are somewhat broadened. Below the direct-transition absorption edge we report the presence of indirect spin-reversing transitions between the Fermi energy sEfd and the extrema of the minority-spin valence and conduction bands, providing a measure of the band edge energies. Both of these edges appear closer to Ef than is seen in well-ordered bulk NiMnSb, with the conduction-band minimum showing weight at only 200 cm−1 above Ef, close enough to have substantial occupation at ambient temperature.

Key words: Optical-Properties; Semiconductor; Injection; Ferromagnets; Disorder; Alloys.

Author: C.E.A. Grigorescu